1. Field of the Invention
The present invention relates to a hybrid vehicle.
2. Description of Related Art
Conventionally, a hybrid vehicle is, for example, provided with an engine, a drive motor, a generator motor, and a planetary gear unit as a differential gear unit, wherein the three gear elements of the planetary gear unit are coupled to the engine, the generator motor, and an output shaft, respectively, and, furthermore, the drive motor is coupled to the output shaft, thereby transmitting part of a power output from the engine to the generator motor and a remainder of the power output from the engine to the output shaft.
When the hybrid vehicle is to be run with the engine stopped, the drive motor is driven mainly and, for a portion of a driving force generated by the drive motor that falls short of a total driving force required for running the hybrid vehicle, the generator motor is driven and a motor torque generated by the generator motor is transmitted through the planetary gear unit to the output shaft, thus supplementing a total power requirement. (See Japanese Patent Application Laid-Open No. HEI 8-295140.)
To prevent the engine from being rotated in a backward direction as the vehicle is driven by the drive motor and the generator motor, a one-way clutch is disposed between the output shaft to which engine rotation is transmitted and a casing.
In the conventional hybrid vehicle, however, a driving force is always supplemented by the generator motor each time the hybrid vehicle is started and the one-way clutch receives a reaction force generated by the driving of the generator motor. The one-way clutch is therefore subjected to a repeated load, resulting in a damage thereof, thus giving rise to such problems as backward rotation and seizure. There is, however, no means of determining whether or not a failure has occurred in the one-way clutch. This aggravates the damage of the one-way clutch.
If, for example, the one-way clutch rotates in the backward direction, it causes the engine to rotate in the backward direction. The terminology xe2x80x9cengine rotate in a backward directionxe2x80x9d is also referred to herein as the xe2x80x9cengine speed is a negative value.xe2x80x9d Backward rotation of the engine could affect engine functions. If, on the other hand, the one-way clutch seizes, not only the engine motoring, which is a condition wherein the engine speed is increased to a level that permits ignition of the engine, is disabled by controlling the drive motor and the generator motor, but also a current supply from the battery to the generator motor is continued. Consequently, there is a possibility of a battery rundown.
Furthermore, the battery cannot be charged by the generator motor, since the engine cannot be started properly.
It is an object of the present invention to solve these problems of the conventional hybrid vehicle and to provide a hybrid vehicle that can determine whether or not a failure has occurred in the one-way clutch.
To achieve the aforementioned object, a hybrid vehicle of the present invention is provided with an engine, a generator motor, an output shaft coupled to a driving wheel, a differential gear unit that is provided with at least three gear elements, the elements coupled to the engine, the generator motor, and the output shaft, respectively, a one-way clutch that is placed in a free state when the engine rotates in a forward direction and to a locked state when the engine begins to rotate in a backward direction, and a failure occurrence determination process means that determines that a failure has occurred in the one-way clutch if an engine speed is a negative value.
In this case, it is determined that a failure has occurred in the one-way clutch if the engine speed is a negative value. The damage of the one-way clutch can therefore be prevented from being aggravated by controlling the engine so as to rotate in the forward direction.
Another hybrid vehicle of the present invention is provided with an engine, a generator motor, an output shaft coupled to a driving wheel, a differential gear unit that is provided with at least three gear elements, the elements coupled to the engine, the generator motor, and the output shaft, respectively, a one-way clutch that is placed in a free state when the engine rotates in a forward direction and in a locked state when the engine begins to rotate in a backward direction, and a failure occurrence determination process means that determines that a failure has occurred in the one-way clutch if the engine speed is a negative value, i.e., if the engine rotates backwards, when the motor torque in a direction of lowering the engine speed is generated by the generator motor.
In this case, it is determined that a failure has occurred in the one-way clutch if the engine speed is a negative value when the motor torque in the direction of lowering the engine speed is generated by the generator motor. The damage of the one-way clutch can therefore be prevented from being aggravated if the generator motor is stopped from generating the motor torque so as to lower the engine speed and the engine is controlled so as to be rotated in the forward direction.
Still another hybrid vehicle of the present invention is further provided with an error process means that, when it is determined that a failure has occurred in the one-way clutch, stops the generator motor from generating a motor torque in a direction of lowering the engine speed i.e., in a direction opposite to the forward engine direction of rotation.
Still another hybrid vehicle of the present invention is provided with an engine, a generator motor, an output shaft coupled to a driving wheel, a differential gear unit that is provided with at least three gear elements, the elements coupled to the engine, the generator motor, and the output shaft, respectively, a one-way clutch that is placed in a free state when the engine rotates in a forward direction and in a locked state when the engine begins to rotate in a backward direction, and a failure occurrence determination process means that determines that a failure has occurred in the one-way clutch if a motor torque generated by the generator motor is greater than a motor torque threshold value and, at the same time, an engine speed is a value less than an engine speed threshold value, when a motor torque in a direction of increasing the engine speed is generated by the generator motor.
In this case, it is determined that a failure has occurred in the one-way clutch if the motor torque generated by the generator motor is greater than the motor torque threshold value and, at the same time, the engine speed is a value less than the engine speed threshold value, when the motor torque in the direction of increasing the engine speed is generated by the generator motor. It is therefore possible to prevent the battery from running down by stopping the engine to start or limiting the motor torque generated by the drive motor.
Still another hybrid vehicle of the present invention is further provided with an error process means that, when it is determined that a failure has occurred in the one-way clutch, stops the engine from being started.
Still another hybrid vehicle of the present invention is further provided with a drive motor that is driven by an electric power obtained from the generator motor and an error process means that, when it is determined that a failure has occurred in the one-way clutch, limits a motor torque generated by the drive motor.
In this case, the motor torque generated by the drive motor is limited. This allows the hybrid vehicle to move to a safe location or to a nearest service shop by driving the drive motor only.
In still another hybrid vehicle of the present invention, the failure occurrence determination process means determines that a failure has occurred in the one-way clutch if the engine speed continues to be the value less than the engine speed threshold value for a predetermined time.
In this case, it is determined that a failure has occurred in the one-way clutch when the engine speed continues to be the above mentioned value for a predetermined time. This can prevent a false determination due to a detection error or the like from being made.